The invention relates to a method and structure for anchoring a floating structure, such as a hydrocarbon storage and/or processing vessel, a tanker, barge, SPAR buoy or a mooring buoy with anchor lines containing large rope sections to the sea bed.
Upon installation of an offshore project, floating production storage and offloading vessels (FPSO), floating production, drilling, storage and offloading vessels (FPDSO), floating production, workover, storage and offloading vessels (FPWSO), Spar buoys, catenary anchor leg mooring (CALM) buoys, semi-submersibles or other hydrocarbon storage and/or processing vessels are moored to the sea bed via anchor lines, and are connected to a subsea oil or gas well via one or more product risers. Especially in water depths of over 300 m, rope anchor lines are used, such as steel wire rope or polyester rope. If these anchor lines become slack during installation, they can bend and kink, such that the anchor lines are weakened, or may even break. Placing the rope anchor lines on the seabed during installation is not preferred in view of possible damage to the anchor lines.
Upon installation, a critical time path can be followed in which the anchor lines, product risers and hydrocarbon production and/or storage vessel need all be installed and hooked up simultaneously prior to production. Alternatively, first installing the anchor lines, followed by hook up of the vessel to the anchor lines and product risers, results in the problem of temporary abandonment and recovery of the anchor lines and consequent damage to the anchor lines.